Experimental data that are used to determine rate coefficients depend not only upon reaction rates but also the physical properties of the measured species. Sensitivity coefficients are presented for the physical parameters of three general experimental techniques: a signal linearly dependent on the concentration of a species, a signal quadratically dependent on concentration, and a schlieren signal, which depends upon a bulk property of the system. With these, both the physical and chemical parameters of a model may be treated on a comparable basis. The similarities and differences between these techniques are illustrated in a simple example of radical formation via first-order precursor decomposition followed by second-order recombination. The results are then applied to two important examples: HZ + 0 2 and CH3 + CH3. In almost all cases, the experimental data contains more information about the physical parameters, such as the optical cross section, than the kinetic rate coefficients. Furthermore, if a physical parameter is not properly treated; strong correlations between it and rate coefficients will introduce significant systematic biases in the rate coefficient. 0